Brainfuck to Ruby compiler

bfr.rb

#!/usr/bin/env ruby

# bfr - brainfuck 2 ruby

# Usage:
# ./bfr "++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>."
# => Hello World!

INDENT = "  "
START_CODE = <<CODE
r=[0]*30000
i=0
def getch()
  system('stty raw -echo')
  STDIN.getc.ord
end

CODE

END_CODE = ""

opcodes = {
  '>' => 'i+=1',
  '<' => 'i-=1',
  '+' => 'r[i]+=1',
  '-' => 'r[i]-=1',
  '.' => 'print r[i].chr',
  ',' => 'r[i]=getch',
  '[' => 'while !r[i].zero?',
  ']' => 'end'
}

bf_program = ARGV[0]

ruby_program = START_CODE + "\n"
keys = opcodes.keys

indent_level = 0
byte = 0
bf_program.split(//).each do |code|
  byte += 1
  raise "Illegal Opcode: '#{code}' at byte #{byte}" unless keys.include?(code)
  indent_level -= 1 if code == ']'
  raise "Unexpected ']' at byte #{byte}" if indent_level < 0
  indentation = INDENT * indent_level
  ruby_program += indentation + opcodes[code] + "\n"
  indent_level += 1 if code == '['
end
raise "Unclosed '[' at end of program" unless indent_level == 0
ruby_program += END_CODE

File.open("brainfuck.ruby", "w") do |file|
  file.puts ruby_program
end

if (system "ruby brainfuck.ruby")
  system "rm brainfuck.ruby"
end